The Big Thing at Apple's 2012 Developer Conference

Here’s the thing about Apple’s Worldwide Developers Conference: It’s not the huge deal it used to be — not for Apple’s top line, anyway.

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Until last year, Apple used it three times in a row as the launch pad for new iPhones. And because the iPhone is the top-selling product in Apple’s portfolio (and among the most profitable), that made WWDC arguably Apple’s most important event of the year.

Recently some subtle things have shifted, though. Instead of unveiling new iPhone hardware at WWDC last year, Apple previewed the upcoming iOS software. Apple also launched iCloud, a service that will stretch across all of Apple’s products, providing storage and other features. In the past, Apple has also spent time talking about Mac software.

So what’s likely to be the big takeaway from this year’s WWDC? Think margins.

Here’s why: A big part of the iPhone’s value is wrapped up in the love and loyalty it inspires in customers. Many carriers are willing to subsidize iPhones to the tune of $450 up front because iPhone customers (a) stick with their carrier longer to buy more accessories and other services, (b) buy bigger data plans, and (c) need less hand-holding.

What makes that possible? Software and services. They drive the loyalty and ease of use that make carriers want to spend a lot on iPhones. And WWDC is shaping up to be the go-to venue for software and services.

What are some things Apple might announce that would help boost or maintain margins?

iCloud upgrades: Right now, iCloud is mainly for basic storage and syncing across various devices. If Apple starts allowing people to easily back up their entire photo libraries in the cloud (for a fee), more people might upgrade to paid accounts.

Facebook iOS integration: Last year’s WWDC brought Twitter integration into iOS 5. Facebook integration this year would be a big point of differentiation vs. Android and Google Plus . Of course, Apple would have to kill or overhaul its Ping social network to get it done — but Tim Cook telegraphed exactly that move a couple weeks ago.

Siri improvement and expansion: If Siri expands beyond the iPhone 4S to, say, the iPad, that would strengthen the overall Apple ecosystem and increase the likelihood that carriers will continue to subsidize products their customers really love.

This isn’t to say WWDC will be completely devoid of revenue-driving announcements. Sites like 9to5Mac are projecting that Apple will introduce four new Mac models, at least two of them laptops. Along with those announcements, I expect to see OS X Mountain Lion make an appearance, along with upgrades to the Mac App Store.

In perspective, Apple sold just over $5 billion worth of Macs last quarter, only slightly more than a year before. At the same time, they sold about $6.6 billion worth of iPads, a category that’s growing much faster. Even if the new models send Mac sales soaring 50% year-over-year, that’ll be just $2.5 billion in additional quarterly revenue. When Apple pulled in $39.2 billion in revenue last quarter, that’s nice, but not much of a bump.

That’s why margins are likely to be the big deal at WWDC this year. Software and services might not be as sexy as new hardware, but they’re what Apple’s profits are made of in the long run.